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Subject: Re: [PATCH v2 2/5] mm,memory_hotplug: Introduce MHP_VMEMMAP_FLAGS
To:     Oscar Salvador <osalvador@suse.de>, akpm@linux-foundation.org
Cc:     mhocko@suse.com, dan.j.williams@intel.com,
        pasha.tatashin@soleen.com, Jonathan.Cameron@huawei.com,
        anshuman.khandual@arm.com, vbabka@suse.cz, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <20190625075227.15193-1-osalvador@suse.de>
 <20190625075227.15193-3-osalvador@suse.de>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <a1e459fe-c48c-b888-7cf3-973fb0684509@redhat.com>
Date:   Tue, 25 Jun 2019 10:31:16 +0200
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On 25.06.19 09:52, Oscar Salvador wrote:
> This patch introduces MHP_MEMMAP_DEVICE and MHP_MEMMAP_MEMBLOCK flags,
> and prepares the callers that add memory to take a "flags" parameter.
> This "flags" parameter will be evaluated later on in Patch#3
> to init mhp_restrictions struct.
> 
> The callers are:
> 
> add_memory
> __add_memory
> add_memory_resource
> 
> Unfortunately, we do not have a single entry point to add memory, as depending
> on the requisites of the caller, they want to hook up in different places,
> (e.g: Xen reserve_additional_memory()), so we have to spread the parameter
> in the three callers.
> 
> The flags are either MHP_MEMMAP_DEVICE or MHP_MEMMAP_MEMBLOCK, and only differ
> in the way they allocate vmemmap pages within the memory blocks.
> 
> MHP_MEMMAP_MEMBLOCK:
> 	- With this flag, we will allocate vmemmap pages in each memory block.
> 	  This means that if we hot-add a range that spans multiple memory blocks,
> 	  we will use the beginning of each memory block for the vmemmap pages.
> 	  This strategy is good for cases where the caller wants the flexiblity
> 	  to hot-remove memory in a different granularity than when it was added.
> 
> 	  E.g:
> 		We allocate a range (x,y], that spans 3 memory blocks, and given
> 		memory block size = 128MB.
> 		[memblock#0  ]
> 		[0 - 511 pfns      ] - vmemmaps for section#0
> 		[512 - 32767 pfns  ] - normal memory
> 
> 		[memblock#1 ]
> 		[32768 - 33279 pfns] - vmemmaps for section#1
> 		[33280 - 65535 pfns] - normal memory
> 
> 		[memblock#2 ]
> 		[65536 - 66047 pfns] - vmemmap for section#2
> 		[66048 - 98304 pfns] - normal memory
> 
> MHP_MEMMAP_DEVICE:
> 	- With this flag, we will store all vmemmap pages at the beginning of
> 	  hot-added memory.
> 
> 	  E.g:
> 		We allocate a range (x,y], that spans 3 memory blocks, and given
> 		memory block size = 128MB.
> 		[memblock #0 ]
> 		[0 - 1533 pfns    ] - vmemmap for section#{0-2}
> 		[1534 - 98304 pfns] - normal memory
> 
> When using larger memory blocks (1GB or 2GB), the principle is the same.
> 
> Of course, MHP_MEMMAP_DEVICE is nicer when it comes to have a large contigous
> area, while MHP_MEMMAP_MEMBLOCK allows us to have flexibility when removing the
> memory.
> 
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> ---
>  drivers/acpi/acpi_memhotplug.c |  2 +-
>  drivers/base/memory.c          |  2 +-
>  drivers/dax/kmem.c             |  2 +-
>  drivers/hv/hv_balloon.c        |  2 +-
>  drivers/s390/char/sclp_cmd.c   |  2 +-
>  drivers/xen/balloon.c          |  2 +-
>  include/linux/memory_hotplug.h | 22 +++++++++++++++++++---
>  mm/memory_hotplug.c            | 10 +++++-----
>  8 files changed, 30 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
> index db013dc21c02..860f84e82dd0 100644
> --- a/drivers/acpi/acpi_memhotplug.c
> +++ b/drivers/acpi/acpi_memhotplug.c
> @@ -218,7 +218,7 @@ static int acpi_memory_enable_device(struct acpi_memory_device *mem_device)
>  		if (node < 0)
>  			node = memory_add_physaddr_to_nid(info->start_addr);
>  
> -		result = __add_memory(node, info->start_addr, info->length);
> +		result = __add_memory(node, info->start_addr, info->length, 0);
>  
>  		/*
>  		 * If the memory block has been used by the kernel, add_memory()
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 07ba731beb42..ad9834b8b7f7 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -516,7 +516,7 @@ static ssize_t probe_store(struct device *dev, struct device_attribute *attr,
>  
>  	nid = memory_add_physaddr_to_nid(phys_addr);
>  	ret = __add_memory(nid, phys_addr,
> -			   MIN_MEMORY_BLOCK_SIZE * sections_per_block);
> +			   MIN_MEMORY_BLOCK_SIZE * sections_per_block, 0);
>  
>  	if (ret)
>  		goto out;
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 3d0a7e702c94..e159184e0ba0 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -65,7 +65,7 @@ int dev_dax_kmem_probe(struct device *dev)
>  	new_res->flags = IORESOURCE_SYSTEM_RAM;
>  	new_res->name = dev_name(dev);
>  
> -	rc = add_memory(numa_node, new_res->start, resource_size(new_res));
> +	rc = add_memory(numa_node, new_res->start, resource_size(new_res), 0);
>  	if (rc) {
>  		release_resource(new_res);
>  		kfree(new_res);
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index 6fb4ea5f0304..beb92bc56186 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -731,7 +731,7 @@ static void hv_mem_hot_add(unsigned long start, unsigned long size,
>  
>  		nid = memory_add_physaddr_to_nid(PFN_PHYS(start_pfn));
>  		ret = add_memory(nid, PFN_PHYS((start_pfn)),
> -				(HA_CHUNK << PAGE_SHIFT));
> +				(HA_CHUNK << PAGE_SHIFT), 0);
>  
>  		if (ret) {
>  			pr_err("hot_add memory failed error is %d\n", ret);
> diff --git a/drivers/s390/char/sclp_cmd.c b/drivers/s390/char/sclp_cmd.c
> index 37d42de06079..f61026c7db7e 100644
> --- a/drivers/s390/char/sclp_cmd.c
> +++ b/drivers/s390/char/sclp_cmd.c
> @@ -406,7 +406,7 @@ static void __init add_memory_merged(u16 rn)
>  	if (!size)
>  		goto skip_add;
>  	for (addr = start; addr < start + size; addr += block_size)
> -		add_memory(numa_pfn_to_nid(PFN_DOWN(addr)), addr, block_size);
> +		add_memory(numa_pfn_to_nid(PFN_DOWN(addr)), addr, block_size, 0);
>  skip_add:
>  	first_rn = rn;
>  	num = 1;
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 37a36c6b9f93..33814b3513ca 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -349,7 +349,7 @@ static enum bp_state reserve_additional_memory(void)
>  	mutex_unlock(&balloon_mutex);
>  	/* add_memory_resource() requires the device_hotplug lock */
>  	lock_device_hotplug();
> -	rc = add_memory_resource(nid, resource);
> +	rc = add_memory_resource(nid, resource, 0);
>  	unlock_device_hotplug();
>  	mutex_lock(&balloon_mutex);
>  
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 0b8a5e5ef2da..6fdbce9d04f9 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -54,6 +54,22 @@ enum {
>  };
>  
>  /*
> + * We want memmap (struct page array) to be allocated from the hotadded range.
> + * To do so, there are two possible ways depending on what the caller wants.
> + * 1) Allocate memmap pages per device (whole hot-added range)
> + * 2) Allocate memmap pages per memblock
> + * The former implies that we wil use the beginning of the hot-added range

s/wil/will/

> + * to store the memmap pages of the whole range, while the latter implies
> + * that we will use the beginning of each memblock to store its own memmap
> + * pages.
> + * Please note that only SPARSE_VMEMMAP implements this feature and some
> + * architectures might not support it even for that memory model (e.g. s390)

Probably rephrase to "This is only a hint, not a guarantee. Only
selected architectures support it with SPARSE_VMEMMAP."

> + */
> +#define MHP_MEMMAP_DEVICE	(1UL<<0)
> +#define MHP_MEMMAP_MEMBLOCK	(1UL<<1)
> +#define MHP_VMEMMAP_FLAGS	(MHP_MEMMAP_DEVICE|MHP_MEMMAP_MEMBLOCK)
> +
> +/*
>   * Restrictions for the memory hotplug:
>   * flags:  MHP_ flags
>   * altmap: alternative allocator for memmap array
> @@ -342,9 +358,9 @@ static inline void __remove_memory(int nid, u64 start, u64 size) {}
>  extern void __ref free_area_init_core_hotplug(int nid);
>  extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
>  		void *arg, int (*func)(struct memory_block *, void *));
> -extern int __add_memory(int nid, u64 start, u64 size);
> -extern int add_memory(int nid, u64 start, u64 size);
> -extern int add_memory_resource(int nid, struct resource *resource);
> +extern int __add_memory(int nid, u64 start, u64 size, unsigned long flags);
> +extern int add_memory(int nid, u64 start, u64 size, unsigned long flags);
> +extern int add_memory_resource(int nid, struct resource *resource, unsigned long flags);
>  extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
>  		unsigned long nr_pages, struct vmem_altmap *altmap);
>  extern bool is_memblock_offlined(struct memory_block *mem);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 4e8e65954f31..e4e3baa6eaa7 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1057,7 +1057,7 @@ static int online_memory_block(struct memory_block *mem, void *arg)
>   *
>   * we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG
>   */
> -int __ref add_memory_resource(int nid, struct resource *res)
> +int __ref add_memory_resource(int nid, struct resource *res, unsigned long flags)
>  {
>  	struct mhp_restrictions restrictions = {};
>  	u64 start, size;
> @@ -1135,7 +1135,7 @@ int __ref add_memory_resource(int nid, struct resource *res)
>  }
>  
>  /* requires device_hotplug_lock, see add_memory_resource() */
> -int __ref __add_memory(int nid, u64 start, u64 size)
> +int __ref __add_memory(int nid, u64 start, u64 size, unsigned long flags)
>  {
>  	struct resource *res;
>  	int ret;
> @@ -1144,18 +1144,18 @@ int __ref __add_memory(int nid, u64 start, u64 size)
>  	if (IS_ERR(res))
>  		return PTR_ERR(res);
>  
> -	ret = add_memory_resource(nid, res);
> +	ret = add_memory_resource(nid, res, flags);
>  	if (ret < 0)
>  		release_memory_resource(res);
>  	return ret;
>  }
>  
> -int add_memory(int nid, u64 start, u64 size)
> +int add_memory(int nid, u64 start, u64 size, unsigned long flags)
>  {
>  	int rc;
>  
>  	lock_device_hotplug();
> -	rc = __add_memory(nid, start, size);
> +	rc = __add_memory(nid, start, size, flags);
>  	unlock_device_hotplug();
>  
>  	return rc;
> 

Apart from that, looks good to me.

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

Thanks,

David / dhildenb